-( Story related, cannot be missed )-
The gate to the bridge to Helheim is barred by two of Helal's guardians, Surtr and Valravn. Surtr awaits behind the right door, one of two you can choose after your skirmish with the Northmen at the gate. Be weary of Surtr's attacks, trying to be on the defensive until you can take one or two swings in. You should notice a blue image building up on Senua's side; this is the Focus gauge building on Druth's mirror. Once you hear the voices tell you to focus to get through Surtr's flames, use R2 to focus (much like you would in the puzzle elements to hear from the Lore Runes or acquire the Puzzle Locks) to slow time down, disrupt his flames, and give you time to hack and slash into him. He's the easier of the two guardians.